Imaging systems are used in a wide variety of applications requiring the acquisition and detection of events within a specified field of view. These events are detected by the reception of their associated electromagnetic radiation, such as light rays. While these imaging systems have been proven to be quite useful in the detection of these events, they have generally employed lenses which are required to have the limiting aperture stop located external to and to the rear of the lenses, usually within a cryogenic dewar. In this configuration, the off-axis light ray bundles strike the receptive medium, such as a bulk silicon detector array, at an angle that varies linearly with the off-axis image location. This characteristic may be undesirable in some applications and techniques involving conventional optics do exist for remedying the situation. The standard procedure is to employ an "immersion lens" in close proximity to the receptive medium.
These conventional immersion lenses have been found, however, to introduce significant amounts of imaging aberrations, primarily in the form of field curvature and lateral color. Compensating for the induced aberrations of these conventional lenses has required extensive modifications to the usual image-forming optics associated with the imaging systems. These conventional immersion lenses cannot simply be added to an existing optical system. Lastly, these conventional immersion lenses have a significant amount of mass, which must be cooled, resulting in a concomitant increase in energy expended by the overall sensor system.